This invention is directed to a method and apparatus for improving the weighing accuracy of hot substances being weighed on sensitive analytical type balances and more particularly the invention is directed to an apparatus and method which reduces or eliminates convection currents generated by the volatilization of moisture and/or solvents from heated substances, thereby enabling accurate weighings to be made without first cooling the substance.
In recent years, analytical procedures have been developed for high speed quantitative analysis of various agricultural commodities, food stuffs, dairy products, paints, coatings, paper products, tobacco and the like which require the volatilization of moisture or solvents from the substance. These procedures utilize microwave heating of a small quantity of material being analyzed to remove various volatiles such as solvents and/or moisture followed by calculations of the amount of moisture, solids or other residuals and losses which are being determined. The methods require initially weighing the substance followed by microwave heating to volatilize low boiling components such as solvents, moisture, etc., followed by reweighing and perhaps other procedural steps. To accomplish these weighings in a rapid and accurate manner, the substance is not removed from the balance but rather weighed in place after each succeeding step. Preferably, the weight of the substance is sensed or measured repeatedly during the microwave heating while volatiles are still being removed from the heated substances and when complete dryness is obtained. Such procedures not only require highly sensitive balances but also sensing the weight while the substance is still hot.
It is well known that heated substances generate convection currents which cause air flows around the heated substance. These air currents substantially affect the weighing accuracy of sensitive electrical balances. To obtain the required accuracy for such analytical procedures, weighing accuracies in the range of plus or minus 0.10 milligrams is often required. At the required degree of accuracy, convection currents can substantially affect the measured results and widen the limits of reproducibility.
It is therefore an object of the present invention to provide a method and apparatus for substantially improving the accuracy of weighing heated substances on sensitive balances.
It is a further object of the present invention to provide an enclosure which arrests convection currents but yet is permeable to microwave radiation and permits the sensing of weights while still subjecting the substance to heating.
It is another object of the present invention to provide an air barrier enclosure which substantially eliminates convection currents generated by heated substances while aiding in the removal of volatiles.
It is yet another object of the present invention to provide a method for reducing or eliminating convection current influences on automatic balance weighings while at the same time permitting the heating of the substance on the balance in situ.
These and other objects of the present invention will become more apparent from the description of the invention which follows.